How to increase neck opening?

I’m about to make the bedtime story pajamas for my daughter who is 10. As the pattern is only sized to 8, and she is big for 10 years old, I want to increase the size of the neck opening. I haven’t made the pattern in several years, so I’m a little uncertain as to how is the best way to go about it. I would really appreciate hearing your thoughts.

On the piece for the front, there are dots to indicate the end point of the shoulder seams. I am considering moving the placement of those dots towards the outside about 1/2″ and re-drawing the slope of the front to make it more open. I realize I also need to do something to the back to make it correspond.

Additionally, I will need to increase the chest size, as her chest matches the “finished” measurements. That seems straightforward- I think I can simply extend the side edge of both front and back pieces by about an inch.

I’m doing all this in a stretch. The sewing shop near my house had no voile or lawn, like I was hoping for and the little old ladies insisted that this cotton/poly stretch was the only fabric one would ever use to make pajamas. Actually, it will probably be good that it’s in a stretch so there is more ease as I’m pretty unsure about how it will all go down.

I would wonder if you made it in stretch whether that would be enough?
My girls wore the size 8 until they were 12.
I don’t have a lot of success sizing up patterns, I find they lose the original look for me but I would wonder about splitting the centre front piece and adding to the middle?
Perhaps split the back at the shoulders to the hem and add a little to the centre back seam?
I am sorry not to be more help.

The Sleepover goes up to a size 12 and I have made those in knit and they fit my 15 year old girls.